U.S. patent application number 14/004576 was filed with the patent office on 2014-01-02 for method and apparatus for handing over mobile cell.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is Byounghoon Kim, Hakseong Kim, Hanbyul Seo. Invention is credited to Byounghoon Kim, Hakseong Kim, Hanbyul Seo.
Application Number | 20140003327 14/004576 |
Document ID | / |
Family ID | 46932094 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140003327 |
Kind Code |
A1 |
Seo; Hanbyul ; et
al. |
January 2, 2014 |
METHOD AND APPARATUS FOR HANDING OVER MOBILE CELL
Abstract
The present invention relates to a wireless communication
system, and more particularly, to a method and an apparatus for
performing a handover related to a mobile cell. A method for a user
equipment handing over a mobile relay, according to one embodiment
of the present invention, can comprise a step of reporting to a
serving base station information on the state of the user equipment
with respect to the mobile relay handover, and a step of handing
over the mobile relay based on a handover command by the serving
base station, the handover being determined based on the state of
the user equipment. As a result, a way for efficiently and
accurately performing the handover related to the mobile cell can
be provided.
Inventors: |
Seo; Hanbyul; (Anyang-si,
KR) ; Kim; Hakseong; (Anyang-si, KR) ; Kim;
Byounghoon; (Anyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seo; Hanbyul
Kim; Hakseong
Kim; Byounghoon |
Anyang-si
Anyang-si
Anyang-si |
|
KR
KR
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
46932094 |
Appl. No.: |
14/004576 |
Filed: |
March 26, 2012 |
PCT Filed: |
March 26, 2012 |
PCT NO: |
PCT/KR2012/002182 |
371 Date: |
September 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61468545 |
Mar 28, 2011 |
|
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Current U.S.
Class: |
370/315 |
Current CPC
Class: |
H04W 36/32 20130101;
H04B 7/18541 20130101; H04W 36/08 20130101; H04W 84/005 20130101;
H04W 88/04 20130101 |
Class at
Publication: |
370/315 |
International
Class: |
H04B 7/185 20060101
H04B007/185 |
Claims
1. A method for performing a mobile relay handover at a user
equipment, the method comprising: reporting information about a
state of the user equipment regarding the mobile relay handover to
a serving base station; and performing the mobile relay handover
based on a handover command received from the serving base station,
the handover command being determined based on the state of the
user equipment by the serving base station.
2. The method according to claim 1, wherein the state of the user
equipment is one of a first state in which the user equipment and a
mobile relay travel in the same predicted route and a second state
in which the user equipment and the mobile relay travel in
different predicted routes.
3. The method according to claim 2, wherein if the mobile relay
handover is a handover from the mobile relay to another base
station, the mobile relay handover is not performed when the state
of the user equipment is the first state and the mobile relay
handover is performed when the state of the user equipment is the
second state.
4. The method according to claim 2, wherein if the mobile relay
handover is a handover from another base station to the mobile
relay, the mobile relay handover is performed when the state of the
user equipment is the first state and the mobile relay handover is
not performed when the state of the user equipment is the second
state.
5. The method according to claim 1, wherein the state of the user
equipment is determined based on at least one of information input
by a user of the user equipment, identification information preset
in the user equipment, and a sensing result of the user
equipment.
6. The method according to claim 5, wherein the information input
by the user of the user equipment is a response to a request for
confirming the state of the user equipment.
7. The method according to claim 5, wherein the preset
identification information includes at least one of information
about a predicted travel route of the mobile relay, identification
information about the mobile relay, identification information
about a transportation means in which the mobile relay is
installed, time information, and place information.
8. The method according to claim 5, wherein the sensing result of
the user equipment is at least one of a result of sensing a signal
from the mobile relay or a device co-located with the mobile relay
and a result of sensing a medium containing information about at
least one of a predicted travel route, a departure time, a
departure location, an arrival time, and an arrival location of the
mobile relay.
9. The method according to claim 1, wherein the state of the user
equipment is one of a first state in which the mobile relay
handover is allowed and a second state in which the mobile relay
handover is prohibited.
10. The method according to claim 1, wherein the mobile relay
handover is a handover from the mobile relay to another base
station or a handover from another base station to the mobile
relay.
11. A method for supporting a mobile relay handover, the method
comprising: receiving information about a state of a user equipment
regarding the mobile relay handover; and determining whether the
mobile relay handover is to be performed based on the state of the
user equipment and transmitting a handover command to the user
equipment.
12. A user equipment for performing a mobile relay handover, the
user equipment comprising: a transmission module for transmitting a
signal to a network; a reception module for receiving a signal from
the network; and a processor for controlling the user equipment
including the transmission module and the reception module, wherein
the processor is configured to report information about a state of
the user equipment regarding the mobile relay handover to a serving
base station through the transmission module, and to perform the
mobile relay handover based on a handover command received from the
serving base station, the handover command being determined based
on the state of the user equipment by the serving base station.
13. A base station for supporting a mobile relay handover, the base
station comprising: a transmission module for transmitting a signal
to a user equipment; a reception module for receiving a signal from
the user equipment; and a processor for controlling the base
station including the transmission module and the reception module,
wherein the processor is configured to receive information about a
state of the user equipment regarding the mobile relay handover
through the reception module, to determine whether the mobile relay
handover is to be performed based on the state of the user
equipment, and to transmit a handover command to the user equipment
through the transmission module.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system, and more particularly, to a method and apparatus for
performing mobile cell-related handover.
BACKGROUND ART
[0002] A relay is an entity that relays signal transmission and
reception between a macro evolved Node B (eNode B or eNB) and a
User Equipment (UE). Relays may be introduced in order to extend
service coverage and increase cell-edge throughput.
[0003] If the position of a relay changes over time, a cell covered
by the relay may have mobility. Thus, the cell may be called a
mobile cell.
Disclosure
Technical Problem
[0004] If a UE performs handover from another cell to a mobile cell
or from a mobile cell to another cell by a conventional handover
procedure, the handover procedure may be unnecessary.
[0005] An object of the present invention devised to solve the
conventional problem is to provide a method for performing mobile
cell-related handover efficiently and accurately.
[0006] It will be appreciated by persons skilled in the art that
the objects that could be achieved with the present invention are
not limited to what has been particularly described hereinabove and
the above and other objects that the present invention could
achieve will be more clearly understood from the following detailed
description.
Technical Solution
[0007] In an aspect of the present invention, a method for
performing a mobile relay handover at a user equipment includes
reporting information about a state of the user equipment regarding
the mobile relay handover to a serving base station, and performing
the mobile relay handover based on a handover command received from
the serving base station, the handover command being determined
based on the state of the user equipment by the serving base
station.
[0008] In another aspect of the present invention, a method for
supporting a mobile relay handover includes receiving information
about a state of a user equipment regarding the mobile relay
handover, and determining whether the mobile relay handover is to
be performed based on the state of the UE and transmitting a
handover command to the user equipment.
[0009] In another aspect of the present invention, a user equipment
for performing a mobile relay handover includes a transmission
module for transmitting a signal to a network, a reception module
for receiving a signal from the network, and a processor for
controlling the user equipment including the transmission module
and the reception module. The processor is configured to report
information about a state of the user equipment regarding the
mobile relay handover to a serving base station through the
transmission module, and to perform the mobile relay handover based
on a handover command received from the serving base station, the
handover command being determined based on the state of the user
equipment by the serving base station.
[0010] In another aspect of the present invention, a base station
for supporting a mobile relay handover includes a transmission
module for transmitting a signal to a user equipment, a reception
module for receiving a signal from the user equipment, and a
processor for controlling the base station including the
transmission module and the reception module. The processor is
configured to receive information about a state of the user
equipment regarding the mobile relay handover through the reception
module, to determine whether the mobile relay handover is to be
performed based on the state of the user equipment, and to transmit
a handover command to the user equipment through the transmission
module.
[0011] The followings are applicable commonly to the embodiments of
the present invention.
[0012] The state of the user equipment may be one of a first state
in which the user equipment and a mobile relay travel in the same
predicted route and a second state in which the user equipment and
the mobile relay travel in different predicted routes.
[0013] If the mobile relay handover is a handover from the mobile
relay to another base station, the mobile relay handover may not be
performed when the state of the user equipment is the first state
and the mobile relay handover may be performed when the state of
the user equipment is the second state.
[0014] If the mobile relay handover is a handover from another base
station to the mobile relay, the mobile relay handover may be
performed when the state of the user equipment is the first state
and the mobile relay handover may not be performed when the state
of the user equipment is the second state.
[0015] The state of the user equipment may be determined based on
at least one of information input by a user of the user equipment,
identification information preset in the user equipment, and a
sensing result of the user equipment.
[0016] The information input by the user of the user equipment may
be a response to a request for confirming the state of the user
equipment.
[0017] The preset identification information may include at least
one of information about a predicted travel route of the mobile
relay, identification information about the mobile relay,
identification information about a transportation means in which
the mobile relay is installed, time information, and place
information.
[0018] The sensing result of the user equipment may be at least one
of a result of sensing a signal from the mobile relay or a device
co-located with the mobile relay and a result of sensing a medium
containing information about at least one of a predicted travel
route, a departure time, a departure location, an arrival time, and
an arrival location of the mobile relay.
[0019] The state of the user equipment may be one of a first state
in which the mobile relay handover is allowed and a second state in
which the mobile relay handover is prohibited.
[0020] The mobile relay handover may be a handover from the mobile
relay to another base station or a handover from another base
station to the mobile relay.
[0021] The foregoing general description and upcoming detailed
description of the present invention are exemplary, intended to
give an additional description of the appended claims.
Advantageous Effects
[0022] According to the present invention, a method for performing
mobile cell-related handover efficiently and accurately can be
provided.
[0023] It will be appreciated by persons skilled in the art that
the effects that can be achieved with the present invention are not
limited to what has been particularly described hereinabove and
other advantages of the present invention will be more clearly
understood from the following detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this application, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention. In the drawings:
[0025] FIG. 1 illustrates the structure of a radio frame;
[0026] FIG. 2 illustrates the structure of a downlink resource grid
for the duration of one downlink slot;
[0027] FIG. 3 illustrates the structure of a downlink subframe;
[0028] FIG. 4 illustrates the structure of an uplink subframe;
[0029] FIG. 5 illustrates the configuration of a Multiple Input
Multiple Output (MIMO) wireless communication system;
[0030] FIG. 6 illustrates resource partitioning for transmission to
a Relay Node (RN);
[0031] FIG. 7 illustrates a signal flow for a handover
procedure;
[0032] FIGS. 8 and 9 illustrate exemplary handover situations that
may result from introduction of a mobile relay;
[0033] FIG. 10 illustrates a signal flow for a method for
performing mobile relay handover according to the present
invention; and
[0034] FIG. 11 is a block diagram of a User Equipment (UE) and an
evolved Node B (eNB or eNode B) according to the present
invention.
[0035] BEST MODE FOR CARRYING OUT THE INVENTION
[0036] The embodiments of the present invention described
hereinbelow are combinations of elements and features of the
present invention. The elements or features may be considered
selective unless otherwise mentioned. Each element or feature may
be practiced without being combined with other elements or
features. Further, an embodiment of the present invention may be
constructed by combining parts of the elements and/or features.
Operation orders described in embodiments of the present invention
may be rearranged. Some constructions or features of any one
embodiment may be included in another embodiment and may be
replaced with corresponding constructions or features of another
embodiment.
[0037] In the present disclosure, a Base Station (BS) is a terminal
node of a network, which communicates directly with a User
Equipment (UE). In some cases, a specific operation described as
performed by the BS may be performed by an upper node of the BS.
Namely, it is apparent that, in a network comprised of a plurality
of network nodes including a BS, various operations performed for
communication with a UE may be performed by the BS, or network
nodes other than the BS.
[0038] The term `BS` may be replaced with the term `fixed station`,
`Node B`, `evolved Node B (eNode B or eNB)`, `Access Point (AP)`,
etc. The term `relay` may be used interchangeably with `Relay Node
(RN)`, `Relay Station (RS)`, etc. The term `terminal` may be
replaced with the term `TIE`, `Mobile Station (MS)`, `Mobile
Subscriber Station (MSS)`, `Subscriber Station (SS)`, etc.
[0039] Specific terms used in the following description are
provided to help the understanding of the present invention. These
specific terms may be replaced with other terms within the scope
and spirit of the present invention.
[0040] In some cases, to prevent the concept of the present
invention from being ambiguous, structures and apparatuses of the
known art will be omitted, or will be shown in the form of a block
diagram based on main functions of each structure and
apparatus.
[0041] The embodiments of the present invention can be supported by
standard documents disclosed for at least one of wireless access
systems such as Institute of Electrical and Electronics Engineers
(IEEE) 802, 3.sup.rd Generation Partnership Project (3GPP), 3GPP
Long Term Evolution (3GPP LTE), LTE-Advanced (LTE-A), and 3GPP2
systems. Steps or parts that are not described to clarify the
technical features of the present invention can be supported by
those documents. Further, all terms as set forth herein can be
explained by the standard documents.
[0042] The embodiments of the present invention can be used in
various wireless access systems such as Code Division Multiple
Access (CDMA), Frequency Division Multiple Access (FDMA), Time
Division Multiple Access (TDMA), Orthogonal Frequency Division
Multiple Access (OFDMA), Single Carrier Frequency Division Multiple
Access (SC-FDMA), etc. CDMA may be implemented as a radio
technology such as Universal Terrestrial Radio Access (UTRA) or
CDMA2000. TDMA may be implemented as a radio technology such as
Global System for Mobile communications/General Packet Radio
Service/Enhanced Data Rates for GSM Evolution (GSM/GPRS/EDGE).
OFDMA may be implemented as a radio technology such as IEEE 802.11
(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA)
etc. UTRA is a part of Universal Mobile Telecommunication System
(UMTS). 3GPP LTE is a part of Evolved-UMTS (E-UMTS) using E-UTRA.
3GPP LTE employs OFDMA for downlink and SC-FDMA for uplink. LTE-A
is an evolution of 3GPP LTE. WiMAX is described by the IEEE 802.16e
standard (Wireless Metropolitan Area Network (WirelessMAN-OFDMA
Reference System) and the IEEE 802.16m standard (WirelessMAN-OFDMA
Advanced System). For clarity, this application focuses on the 3GPP
LTE/LTE-A system. However, the technical features of the present
invention are not limited thereto.
[0043] With reference to FIG. 1, the structure of a radio frame
will be described below.
[0044] In a cellular Orthogonal Frequency Division Multiplexing
(OFDM) wireless packet communication system, Uplink/Downlink
(UL/DL) data packets are transmitted in subframes. One subframe is
defined as a predetermined time interval including a plurality of
OFDM symbols. The 3GPP LTE standard supports a type 1 radio frame
structure applicable to Frequency Division Duplex (FDD) and a type
2 radio frame structure applicable to Time Division Duplex
(TDD).
[0045] FIG. 1(a) is a diagram illustrating the structure of the
type 1 radio frame. A downlink radio frame includes 10 subframes,
each subframe including two slots in the time domain. A time
required for transmitting one subframe is defined as a Transmission
Time Interval (TTI). For example, one subframe may be 1 ms long and
one slot may be 0.5 ms long. One slot includes a plurality of OFDM
symbols in the time domain and a plurality of Resource Blocks (RBs)
in the frequency domain. Since the 3GPP LTE system uses OFDMA on
DL, an OFDM symbol is one symbol period. The OFDM symbol may be
called an SC-FDMA symbol or symbol period. An RB is a resource
allocation unit including a plurality of contiguous subcarriers in
one slot.
[0046] The number of OFDM symbols included in one slot may be
changed according to the configuration of a Cyclic Prefix (CP).
There are two types of CPs, extended CP and normal CP. For example,
if each OFDM symbol is configured to include a normal CP, one slot
may include 7 OFDM symbols. If each OFDM symbol is configured to
include an extended CP, the length of an OFDM symbol is increased
and thus the number of OFDM symbols included in one slot is less
than that in the case of a normal CP. In the case of the extended
CP, for example, one slot may include 6 OFDM symbols. If a channel
state is instable as is the case with a fast UE, the extended CP
may be used in order to further reduce inter-symbol
interference.
[0047] In the case of the normal CP, since one slot includes 7 OFDM
symbols, one subframe includes 14 OFDM symbols. The first two or
three OFDM symbols of each subframe may be allocated to a Physical
Downlink Control Channel (PDCCH) and the remaining OFDM symbols may
be allocated to a Physical Downlink Shared Channel (PDSCH).
[0048] FIG. 1(b) illustrates the structure of the type 2 radio
frame. The type 2 radio frame includes two half frames, each half
frame including 5 subframes, a Downlink Pilot Time Slot (DwPTS), a
Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS). One
subframe is divided into two slots. The DwPTS is used for initial
cell search, synchronization, or channel estimation at a UE, and
the UpPTS is used for channel estimation and UL transmission
synchronization with a UE at an eNB. The GP is used to cancel UL
interference between UL and DL, caused by the multi-path delay of a
DL signal. One subframe includes two slots irrespective of the type
of a radio frame.
[0049] The structures of radio frames are only exemplary.
Accordingly, the number of subframes in a radio frame, the number
of slots in a subframe, and the number of symbols in a slot may be
changed in various manners.
[0050] FIG. 2 illustrates the structure of a DL resource grid for
the duration of one DL slot. A DL slot has 7 OFDM symbols in the
time domain and an RB includes 12 subcarriers in the frequency
domain, which does not limit the present invention. For example, a
DL slot includes 7 OFDM symbols in a subframe with normal CPs,
whereas a DL slot includes 6 OFDM symbols in a subframe with
extended CPs. Each element of the resource grid is referred to as a
Resource Element (RE). An RB includes 12.times.7 REs. The number of
RBs in a DL slot, N.sup.DL depends on a DL transmission bandwidth.
A UL slot may have the same structure as a DL slot.
[0051] FIG. 3 illustrates the structure of a DL subframe. Up to
three OFDM symbols at the start of the first slot of a DL subframe
are used as a control region to which control channels are
allocated and the other OFDM symbols of the DL subframe are used as
a data region to which a PDSCH is allocated. DL control channels
defined for the 3GPP LTE system include a Physical Control Format
Indicator Channel (PCFICH), a Physical Downlink Control Channel
(PDCCH), and a Physical Hybrid automatic repeat request (ARQ)
Indicator Channel (PHICH). The PCFICH is located in the first OFDM
symbol of a subframe, carrying information about the number of OFDM
symbols used for transmission of control channels in the subframe.
The PHICH delivers an HARQ ACKnowledgment/Negative ACKnowledgment
(ACK/NACK) signal as a response to a UL transmission. Control
information carried on the PDCCH is called Downlink Control
Information (DCI). The DCI transports UL scheduling information, DL
scheduling information, or UL transmission power control commands
for UE groups. The PDCCH delivers information about resource
allocation and a transport format for a Downlink Shared Channel
(DL-SCH), resource allocation information about an Uplink Shared
Channel (UL-SCH), paging information of a Paging Channel (PCH),
system information on the DL-SCH, information about resource
allocation for a higher-layer control message such as a random
access response transmitted on the PDSCH, a set of transmission
power control commands for individual UEs of a UE group,
transmission power control information, Voice Over Internet
Protocol (VoIP) activation information, etc. A plurality of PDCCHs
may be transmitted in the control region. A UE may monitor a
plurality of PDCCHs. A PDCCH is formed by aggregation of one or
more consecutive Control Channel Elements (CCEs). A CCE is a
logical allocation unit used to provide a PDCCH at a coding rate
based on the state of a radio channel. A CCE includes a plurality
of RE Groups (REGs). The format of a PDCCH and the number of
available bits for the PDCCH are determined according to the
relationship between the number of CCEs and a coding rate provided
by the CCEs. An eNB determines a PDCCH format according to DCI
transmitted to a UE and adds a Cyclic Redundancy Check (CRC) to
control information. The CRC is masked by an Identifier (ID) known
as a Radio Network Temporary Identifier (RNTI) according to the
owner or usage of the PDCCH. If the PDCCH is destined for a
specific UE, the CRC may be masked by a cell-RNTI (C-RNTI) of the
UE. If the PDCCH carries a paging message, the CRC of the PDCCH may
be masked by a Paging Indicator Identifier (P-RNTI). If the PDCCH
carries system information, particularly, a System Information
Block (SIB), its CRC may be masked by a system information ID and a
System Information RNTI (SI-RNTI). To indicate that the PDCCH
carries a random access response to a random access preamble
transmitted by a UE, its CRC may be masked by a Random Access-RNTI
(RA-RNTI).
[0052] FIG. 4 illustrates the structure of a UL subframe. A UL
subframe may be divided into a control region and a data region in
the frequency domain. A Physical Uplink Control Channel (PUCCH)
carrying uplink control information is allocated to the control
region and a Physical Uplink Shared Channel (PUSCH) carrying user
data is allocated to the data region. To maintain a single carrier
property, a UE does not transmit a PUSCH and a PUCCH
simultaneously. A PUCCH for a UE is allocated to an RB pair in a
subframe. The RBs of the RB pair occupy different subcarriers in
two slots. Thus it is said that the RB pair allocated to the PUCCH
is frequency-hopped over a slot boundary.
[0053] Modeling of Multiple Input Multiple Output (MIMO) System
FIG. 5 illustrates the configuration of a MIMO wireless
communication system.
[0054] Referring to FIG. 5(a), when the number of Transmission (Tx)
antennas and the number of Reception (Rx) antennas are increased to
N.sub.T and N.sub.R, respectively at both a transmitter and a
receiver, a theoretical channel transmission capacity increases in
proportion to the number of antennas, compared to the use of a
plurality of antennas at only one of the transmitter and the
receiver. Therefore, transmission rate and frequency efficiency are
remarkably increased. Along with the increase of channel
transmission capacity, the transmission rate may be increased in
theory to the product of a maximum transmission rate R, that may be
achieved with a single antenna and a rate increase rate R.
R.sub.i=min(N.sup.T,N.sub.R) [Equation 1]
[0055] For instance, a MIMO communication system with four Tx
antennas and four Rx antennas may achieve a four-fold increase in
transmission rate theoretically, relative to a single-antenna
wireless communication system. Since the theoretical capacity
increase of the MIMO wireless communication system was verified in
the middle 1990s, many techniques have been actively developed to
increase data rate in real implementation. Some of the techniques
have already been reflected in various wireless communication
standards including standards for 3G mobile communications,
future-generation Wireless Local Area Network (WLAN), etc.
[0056] Concerning the research trend of MIMO up to now, active
studies are underway in many respects of MIMO, inclusive of studies
of information theory related to calculation of multi-antenna
communication capacity in diverse channel environments and multiple
access environments, studies of measuring MIMO radio channels and
MIMO modeling, studies of time-space signal processing techniques
to increase transmission reliability and transmission rate,
etc.
[0057] Communication in a MIMO system with N.sub.T T.sub.x antennas
and N.sub.R R.sub.x antennas will be described in detail through
mathematical modeling.
[0058] Regarding a transmission signal, up to N.sub.T pieces of
information can be transmitted through the N.sub.T T.sub.x
antennas, as expressed as the following vector.
s=.left brkt-bot.s.sub.1, s.sub.2, . . . , s.sub.N.sub.T.right
brkt-bot..sup.T [Equation 2]
[0059] A different transmission power may be applied to each piece
of transmission information, s.sub.1, s.sub.2, . . . ,
s.sub.N.sub.T. Let the transmission power levels of the
transmission information be denoted by P.sub.1, P.sub.2, . . . ,
P.sub.N.sub.T, respectively. Then the transmission power-controlled
transmission information vector may be given as
s=[s.sub.1, s.sub.2, . . . , s.sub.N.sub.T].sup.T=[P.sub.1s.sub.1,
P.sub.2s.sub.2, . . . , P.sub.N.sub.Ts.sub.N.sub.T].sup.T [Equation
3]
[0060] The transmission power-controlled transmission information
vector s may be expressed as follows, using a diagonal matrix P of
transmission power.
s ^ = [ P 1 0 P 2 0 P N T ] [ s 1 s 2 s N T ] = Ps [ Equation 4 ]
##EQU00001##
[0061] N.sub.T transmission signals x.sub.1, x.sub.2, . . . ,
x.sub.N.sub.T may be generated by multiplying the transmission
power-controlled information vectors s by a weight matrix W. The
weight matrix W functions to appropriately distribute the
transmission information to the Tx antennas according to
transmission channel states, etc. These N.sub.T transmission
signals x.sub.1, x.sub.2, . . . , x.sub.N.sub.T are represented as
a vector x, which may be determined by
x = [ x 1 x 2 x i x N T ] = [ w 11 w 12 w 1 N T w 21 w 22 w 2 N T w
i 1 w i 2 w iN T w N T 1 w N T 2 w N T N T ] [ s ^ 1 s ^ 2 s ^ j s
^ N T ] = W s ^ = WPs [ Equation 5 ] ##EQU00002##
[0062] Here, w.sub.ij denotes a weight between a j.sup.th piece of
information and an i.sup.th Tx antenna.
[0063] Given N.sub.R Rx antennas, signals received at the Rx
antennas, y.sub.1, y.sub.2, . . . , y.sub.N.sub.R may be
represented as the following vector.
y=[y.sub.1, y.sub.2, . . . , y.sub.N.sub.R].sup.T [Equation 6]
[0064] When channels are modeled in the MIMO wireless communication
system, they may be distinguished according to the indexes of Tx
and Rx antennas. A channel between a j.sup.th Tx antenna and an
i.sup.th Rx antenna is denoted by h.sub.ij. One thing to note
herein is that the index of an Rx antenna precedes the index of a
Tx antenna in h.sub.ij.
[0065] FIG. 5(b) illustrates channels from N.sub.T Tx antennas to
an i.sup.th Rx antenna. The channels may be collectively
represented as a vector or a matrix. Referring to FIG. 5(b), the
channels from the N.sub.T Tx antennas to the i.sup.th Rx antenna
may be expressed as [Equation 7].
h.sub.i.sup.T=[h.sub.i1, h.sub.i2, . . . , h.sub.iN.sub.T]
[Equation 7]
[0066] Hence, all channels from the N.sub.T Tx antennas to the
N.sub.R Rx antennas may be expressed as the following matrix.
H = [ h 1 T h 2 T h i T h N R T ] = [ h 11 h 12 h 1 N T h 21 h 22 h
2 N T h i 1 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ Equation 8 ]
##EQU00003##
[0067] Actual channels experience the above channel matrix H and
then are added with Additive White Gaussian Noise (AWGN). The AWGN
n.sub.1, n.sub.2, . . . , n.sub.N.sub.R added to the N.sub.R Rx
antennas is given as the following vector.
n=[n.sub.1, n.sub.2, . . . , n.sub.N.sub.R].sup.T [Equation 9]
[0068] From the above mathematical modeling, the received signal
vector is given as
y = [ y 1 y 2 y i y N R ] = [ h 11 h 12 h 1 N T h 21 h 22 h 2 N T h
i 1 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ x 1 x 2 x j x N T ]
+ [ n 1 n 2 n i n N R ] = Hx + n [ Equation 10 ] ##EQU00004##
[0069] The numbers of rows and columns in the channel matrix H
representing channel states are determined according to the numbers
of Rx and Tx antennas. Specifically, the number of rows in the
channel matrix H is equal to the number of Rx antennas, N.sub.R and
the number of columns in the channel matrix H is equal to the
number of Tx antennas, N.sub.T. Hence, the channel matrix H is an
N.sub.R.times.N.sub.T matrix.
[0070] The rank of a matrix is defined as the smaller between the
number of independent rows and the number of independent columns in
the matrix. Accordingly, the rank of the matrix is not larger than
the number of rows or columns of the matrix. The rank of the
channel matrix H, rank(H) satisfies the following constraint.
rank(H).ltoreq.min(N.sub.T, N.sub.R) [Equation 11]
[0071] The rank of a matrix may also be defined as the number of
non-zero eigenvalues, when the matrix is decomposed by EigenValue
Decomposition (EVD). Similarly, the rank of a matrix may be defined
as the number of non-zero singular values, when the matrix is
decomposed by Singular Value Decomposition (SVD). Therefore, the
rank of a channel matrix may be the maximum number of different
pieces of information that can be transmitted on a physical
channel, in its physical meaning.
[0072] In MIMO transmission, the term `rank` is the number of paths
in which signals are independently transmitted, and the term
`number of layers` is the number of signal streams transmitted
through respective paths. In general, since a transmitter transmits
as many layers as the rank of signal transmission, the rank has the
same meaning as the number of layers, unless otherwise noted.
[0073] Coordinated Multi-Point (CoMP) To satisfy enhanced system
performance requirements for the 3GPP LTE-A system, CoMP
transmission and reception technology (co-MIMO, collaborative MIMO
or network MIMO) has been proposed. The CoMP technology can
increase the performance of UEs located at a cell edge and an
average sector throughput.
[0074] It is known that Inter-Cell Interference (ICI) generally
degrades the performance of a UE at a cell edge and an average
sector throughput in a multi-cellular environment with a frequency
reuse factor of 1. To reduce ICI, a simple ICI mitigation technique
such as UE-specific power control-based Fractional Frequency Reuse
(FFR) is used in the legacy LTE system. However, it may be
preferred to reduce the ICI or reuse the ICI as a desired signal
for the UE, rather than to decrease the utilization of frequency
resources per cell. For this purpose, CoMP transmission techniques
may be adopted.
[0075] DL CoMP schemes are classified largely into Joint Processing
(JP) and Coordinated Scheduling/Beamforming (CS/CB).
[0076] In the JP scheme, each point (eNB) of CoMP cooperation units
may use data. The CoMP cooperation units refer to a set of eNBs
participating in a CoMP transmission operation. The JP scheme is
further branched into joint transmission and dynamic cell
selection.
[0077] Joint transmission is a technique of transmitting PDSCHs
from a plurality of points (a part or all of CoMP cooperation
units) at one time. That is, a plurality of transmission points may
simultaneously transmit data to a single UE. The joint transmission
scheme can improve the quality of a received signal coherently or
non-coherently and actively eliminate interference with other UEs,
as well.
[0078] Dynamic cell selection is a technique of transmitting a
PDSCH from one point (of CoMP cooperation units) at one time. That
is, one point of the CoMP cooperation units transmits data to a
single UE at a given time point, while the other points of the CoMP
cooperation units do not transmit data to the UE at the time point.
A point to transmit data to a UE may be dynamically selected.
[0079] In the CS/CB scheme, CoMP cooperation units may perform
cooperative beamforming for data transmission to a single UE. While
only a serving cell transmits data to the UE, user
scheduling/beamforming may be determined through coordination among
cells of the CoMP cooperation units.
[0080] UL CoMP reception refers to UL reception of a transmitted
signal through coordination at a plurality of geographically
separated points. UL CoMP schemes include Joint Reception (JR) and
Coordinated Scheduling/Beamforming (CS/CB).
[0081] In JR, a plurality of reception points receive a signal
transmitted on a PUSCH. CS/CB is a technique in which while only
one point receives a PUSCH, user scheduling/beamforming is
determined through coordination among the cells of CoMP cooperation
units.
[0082] In the CoMP system, multi-cellular eNBs may jointly support
data transmission for a UE. Further, since the eNBs simultaneously
support one or more UEs in the same radio frequency resources,
system performance can be increased. The eNBs may perform Space
Division Multiple Access (SDMA) based on channel state information
between the eNBs and the UE.
[0083] A serving eNB and one or more cooperative eNBs are connected
to a scheduler through a backbone network in the CoMP system. The
scheduler may receive feedback channel information about channel
states between each UE and cooperative eNBs as measured by the eNBs
through the backbone network and operate based on the channel
information. For example, the scheduler may schedule cooperative
MIMO information for the serving eNB and one or more cooperative
eNBs. That is, the scheduler may directly transmit a command
related to a cooperative MIMO operation to each eNB.
[0084] As described above, the CoMP system may be regarded as a
virtual MIMO system designed by grouping a plurality of cells.
Basically, a MIMO communication scheme using multiple antennas may
apply to the CoMP system.
[0085] DL Channel State Information (CSI) Feedback
[0086] MIMO schemes may be classified into open-loop MIMO and
closed-loop MIMO. In open-loop MIMO, a MIMO transmitter performs
MIMO transmission without receiving a CSI feedback from a MIMO
receiver. On the other hand, the MIMO transmitter receives a CSI
feedback from the MIMO receiver and performs MIMO transmission
based on the CSI feedback in closed-loop MIMO. To achieve a
multiplexing gain through MIMO Tx antennas, the transmitter and the
receiver each may perform beamforming based on CSI in the
closed-loop MIMO scheme. To enable the receiver (e.g. a UE) to feed
back CSI, the transmitter (e.g. an eNB) may allocate a UL control
channel or a UL shared channel to the receiver.
[0087] A CSI feedback may include a Rank Indication (RI), a
Precoding Matrix Index (PMI), and a Channel Quality Indicator
(CQI).
[0088] An RI is information about a channel rank. The channel rank
is the maximum number of layers (or streams) that may carry
different information in the same time-frequency resources. Because
the rank is determined mainly according to the long-term fading of
a channel, the RI may be fed back in a longer period (i.e. less
frequently) than a PMI and a CQI.
[0089] A PMI is information about a precoding matrix used for
transmission of a transmitter, reflecting the spatial
characteristics of channels. Precoding refers to mapping
transmission layers to Tx antennas. A layer-antenna mapping
relationship may be determined according to a precoding matrix. The
PMI is the index of an eNB precoding matrix preferred by the UE,
selected based on a metric such as Signal-to-Interference plus
Noise Ratio (SINR), etc. In order to reduce the feedback overhead
of precoding information, the transmitter and the receiver may
share a codebook with a plurality of precoding matrices and the
receiver may feed back only the index of a specific precoding
matrix in the codebook.
[0090] A CQI is information representing a channel quality or a
channel strength. The CQI may be expressed as a predetermined
Modulation Coding Scheme (MCS). That is, a feedback CQI index
indicates a corresponding modulation scheme and coding rate. In
general, the CQI reflects a reception SINR that can be achieved
when an eNB configures spatial channels using a PMI.
[0091] A system supporting an extended antenna configuration (e.g.
an LTE-A system) considers achievement of an additional multi-user
diversity by the use of MU-MIMO. Due to the existence of
interference channels between UEs multiplexed in an antenna domain
in MU-MIMO, it is necessary to avoid interference with other UEs,
when an eNB transmits a DL signal to one of multiple UEs based on a
CSI feedback received from the one UE. Accordingly, more accurate
CSI than in Single User MIMO (SU-MIMO) should be fed back for a
reliable MU-MIMO operation.
[0092] For more accurate measurement and reporting of CSI, a new
CSI feedback scheme may be adopted by modifying conventional CSI
including an RI, a PMI, and a CQI. For example, precoding
information fed back from the receiver may be indicated by a set of
two PMIs. One of the two PMIs (PMI 1) has a long-term and/or
wideband property, referred to as W1, whereas the other PMI (PMI 2)
has a short-term and/or subband property, referred to as W2. A
final PMI may be determined by combining W1 and W2 (or a function
of W1 and W2). For example, let the final PMI be denoted by W. Then
W=W1*W2 or W=W2*W1.
[0093] W1 reflects the average frequency and/or time
characteristics of channels. In other words, W1 may be defined as
CSI that reflects long-term channel characteristics in time,
wideband channel characteristics in frequency, or both long-term
channel characteristics in time and wideband channel
characteristics in frequency. To represent these characteristics of
W1, W1 will be referred to as long term-wideband CSI (or a long
term-wideband PMI).
[0094] Compared to W1, W2 reflects relatively instantaneous channel
characteristics. In other words, W2 may be defined as CSI that
reflects short-term channel characteristics in time, subband
channel characteristics in frequency, or both short-term channel
characteristics in time and subband channel characteristics in
frequency. To represent these characteristics of W2, W2 will be
referred to as short term-subband CSI (or a short term-subband
PMI).
[0095] To determine a final precoding matrix W with two pieces of
information having different characteristics representing channel
states (e.g. W1 and W2), separate codebooks with precoding matrices
representing channel information having different characteristics
(e.g. a first codebook for W1 and a second codebook for W2) need to
be configured. These codebooks may be referred to as hierarchical
codebooks. Determination of a final codebook using hierarchical
codebooks is called hierarchical codebook transformation.
[0096] For example, the long-term covariance matrix of channels
expressed as [Equation 12] may be used for hierarchical codebook
transformation.
W=norm(W1W2) [Equation 12]
[0097] In [Equation 12], W1 (i.e. the long term-wideband PMI) is an
element (i.e. a codeword) of a codebook (e.g. the first codebook)
designed to reflect long term-wideband channel information. That
is, W1 is a precoding matrix included in the first codebook
reflecting long term-wideband channel information. On the other
hand, W2 (i.e. the short term-subband PMI) is a codeword of a
codebook (e.g. the second codebook) designed to reflect long
term-wideband channel information. That is, W2 is a precoding
matrix included in the second codebook reflecting short
term-subband channel information. W is a codeword of a final
codebook. norm(A) is a matrix obtained by normalizing the norm of
each column of matrix A to 1.
[0098] W1 and W2 may have the structures expressed as [Equation
13], by way of example.
W 1 ( i ) = [ X i 0 0 X i ] W 2 ( j ) = [ e M k e M l .alpha. j e M
k .beta. j e M l e M m .gamma. j e M m ] r columns ( if rank = r )
[ Equation 13 ] ##EQU00005##
[0099] In [Equation 13], W1 may be defined as a block diagonal
matrix in which each block is an identical matrix X.sub.i. One
block X.sub.i may be defined as an (N.sub.t/2)xM matrix where
N.sub.t is the number of Tx antennas. e.sub.M.sup.p of W2 (p=k, l,
. . . , m) is an Mx1 vector where a p.sup.th element of the M
vector elements is 1 and the other elements are 0. If e.sub.M.sup.p
is multiplied by W1, a p.sup.th column is selected from among the
columns of W1. Thus this vector may be referred to as a selection
vector. As the value of M increases, the number of feedback vectors
transmitted at one time is increased to represent long
term/wideband channels. Consequently, feedback accuracy is also
increased. However, a larger M value leads to a decrease in the
codebook size of W1 that is less frequently fed back, and an
increase in the codebook size of W2 that is more frequently fed
back. As a result, feedback overhead is increased. That is,
feedback overhead and feedback accuracy are in a tradeoff
relationship. Accordingly, the value of M may be determined such
that feedback overhead is not too much, while feedback accuracy is
maintained at an appropriate level. In W2, .alpha..sub.j,
.beta..sub.j, and .gamma..sub.j represent predetermined phase
values. In [Equation 13], l.ltoreq.k, l, m.ltoreq.M where k, l, and
m are integers.
[0100] The codebook structures of [Equation 13] are designed so as
to reflect correlation characteristics between channels, if
cross-polarized (X-pol) antennas are arranged densely (in general,
the distance between adjacent antennas is equal to or less than a
half of a signal wavelength). Exemplary cross-polarized antenna
configurations are listed in [Table 1] below.
TABLE-US-00001 TABLE 1 2Tx cross-polarized antenna configuration
##STR00001## 4Tx cross-polarized antenna configuration ##STR00002##
8Tx cross-polarized antenna configuration ##STR00003##
[0101] Referring to [Table 1], the 8Tx cross-polarized antenna
configuration groups eight antennas into two groups having
different polarizations. The antennas of antenna group 1 (antennas
1, 2, 3 and 4) have the same polarization (e.g. vertical
polarization) and the antennas of antenna group 2 (antennas 5, 6, 7
and 8) have the same polarization (e.g. horizontal polarization).
The two antenna groups are co-located. For example, antennas 1 and
5 may be co-located, antennas 2 and 6 may be co-located, antennas 3
and 7 may be co-located, and antennas 4 and 8 may be co-located. In
other words, the antennas of each antenna group have the same
polarization, like a Uniform Linear Array (LUA) and the
correlations between antennas in each antenna group have a linear
phase increment property. The correlation between the antenna
groups is characterized by phase rotation.
[0102] Considering that a codebook is eventually quantized values
of channels, it is necessary to design a codebook based on real
channel characteristics. To verify that real channel
characteristics are reflected in the codewords of the codebooks
designed as illustrated in [Equation 13], a rank-1 codebook will be
described as an example. [Equation 14] describes a final codeword W
determined to be the product of a codeword W1 and a codeword W2,
for rank 1.
W 1 ( i ) * W 2 ( j ) = [ X i ( k ) .alpha. j X i ( k ) ] [
Equation 14 ] ##EQU00006##
[0103] In [Equation 14], the final codeword is expressed as an
N.sub.tx1 vector divided into an upper vector x.sub.i(k) and a
lower vector .alpha..sub.ix.sub.t(k). The upper vector x.sub.t(k)
represents the correlation characteristics of the horizontal
polarization antenna group of cross-polarized antennas and the
lower vector .alpha..sub.jx.sub.t(k) represents the correlation
characteristics of the vertical polarization antenna group of
cross-polarized antennas. x.sub.t(k) may be expressed as a vector
(e.g. a Discrete Fourier Transform (DFT) matrix) having the linear
phase increment property, reflecting the correlation
characteristics between antennas in each antenna group.
[0104] With the use of the above-described codebooks, a more
accurate channel feedback is possible than with the use of a single
codebook. Therefore, highly accurate channel feedback enables a
single-cell MU-MIMO operation. For a similar reason, highly
accurate channel feedback is required for a CoMP operation. For
example, in CoMP JT, a plurality of eNBs transmit the same data to
a specific UE through cooperation. In theory, the CoMP JT system
may be regarded as a MIMO system with a plurality of geographically
distributed antennas. That is, an MU-MIMO operation in CoMP JT also
requires high accuracy of channel information to avoid interference
between co-scheduled UEs, like a single-cell MU-MIMO operation.
CoMP CB also requires high accuracy of channel information to avoid
interference that a neighbor cell causes to a serving cell.
[0105] Relay Node (RN)
[0106] Use of RNs may be considered, for example, for the purpose
of extending the coverage of high data rates, enhancing group
mobility, deploying a temporary network, improving cell-edge
throughput, and/or providing network coverage to a new area.
[0107] An RN forwards data between an eNB and a UE. Two types of
links having different characteristics in respective carrier
frequency bands (a backhaul link and an access link) are
established for the RN. The eNB may cover a donor cell. The RN is
connected wirelessly to a wireless access network through the donor
cell.
[0108] If the backhaul link between the eNB and the RN uses a DL
frequency band or DL subframe resources, it is called a backhaul
DL. If the backhaul link uses a UL frequency band or UL subframe
resources, it is called a backhaul UL. The frequency bands are FDD
resources and the subframes are TDD resources Likewise, if the
access link between the RN and the UE(s) uses a DL frequency band
or DL subframe resources, it is called an access DL. If the access
link uses a UL frequency band or UL subframe resources, it is
called an access UL.
[0109] The functions of UL reception and DL reception are required
for an eNB and the functions of UL transmission and DL reception
are required for a UE. For an RN, the functions of backhaul UL
transmission to an eNB, access UL reception from a UE, backhaul DL
reception from the eNB, and access DL transmission to the UE are
required.
[0110] With respect to the RN's usage of a frequency band (or
spectrum), its operation can be classified as `in-band` and
`out-band`. For an in-band RN, a backhaul link shares the same
frequency band with an access link. If the backhaul link and the
access link operate in different frequency bands, the RN is an
out-band RN. In both in-band and out-band relaying, a UE
(hereinafter, referred to as a legacy UE) operating in the
conventional LTE system such as one conforming to Release-8 should
be able to access a donor cell.
[0111] Depending on whether a UE is aware of the existence of an
RN, RNs may be classified into a transparent RN and a
non-transparent RN. If the UE does not perceive whether it
communicates with a network via an RN, the RN is a transparent RN.
In contrast, if the UE perceives whether it communicates with a
network via an RN, the RN is a non-transparent RN.
[0112] In relation to control of RNs, RNs may be classified into an
RN configured as a part of a donor cell and an RN that
self-controls a cell.
[0113] The former RN may have an RN ID, although it does not have
its own cell ID. If at least a part of Radio Resource Management
(RRM) is controlled by an eNB covering the donor cell, the RN is
regarded as configured as a part of the donor cell (even though the
other parts of the RRM reside in the RN). Preferably, this RN can
support legacy UEs. For instance, smart repeaters,
decode-and-forward relays, Layer 2 (L2) relays, and Type-2 relays
form a part of a donor cell.
[0114] The latter RN controls one or more cells. The cells are
allocated their unique physical cell IDs and they may use the same
RRM mechanism. From the viewpoint of a UE, there is no distinction
between accessing a cell controlled by an RN and accessing a cell
controlled by a macro eNB. Preferably, a cell controlled by this
type of RN may support legacy UEs. For example, RNs of this type
include self-backhauling RNs, Layer 3 (L3) relays, Type-1 relays,
and Type-1a relays.
[0115] A Type-1 relay is an in-band RN that controls a plurality of
cells. Each of the plurality of cells appears to a UE as a separate
cell distinct from a donor cell. The plurality of cells have their
own physical cell IDs (as defined in LTE Release-8) and the RN can
transmit its own synchronization channel, Reference Signals (RSs),
etc. During a single-cell operation, a UE may receive scheduling
information and an HARQ feedback directly from the RN and transmit
its control channels (a Scheduling Request (SR), a CQI, an
ACK/NACK, etc.) to the RN. The Type-1 relay appears as a legacy eNB
(operating in conformance to LTE Release-8) to a legacy UE
(conforming to LTE Release-8). That is, the Type-1 relay has
backward compatibility. On the other hand, to LTE-A UEs, the Type-1
relay appears different from a legacy eNB. Thus the Type-1 relay
can enhance performance.
[0116] Except for its out-band operation, a Type-1a relay has the
same features as the Type-1 relay. The Type-1a relay may be
configured such that the influence of its operation on an L1
operation is minimized or eliminated.
[0117] A Type-2 relay is an in-band RN that does not have its own
physical cell ID and thus does not form a new cell. Since the
Type-2 relay is transparent to legacy UEs, the legacy UEs do not
notice the existence of the Type-2 relay. The Type-2 relay can
transmit a PDSCH but does not transmit at least a Common Reference
Signal (CRS) and a PDCCH.
[0118] In order to allow in-band relaying, some resources in the
time-frequency domain should be set aside for a backhaul link and
these resources may be configured not to be used for an access
link. This is called resource partitioning.
[0119] A description will be given of the general principle of
resource partitioning at an RN. A backhaul DL and an access DL may
be TDM-multiplexed in one carrier frequency (that is, only one of
the backhaul DL and the access DL is active at a specific time).
Similarly, a backhaul UL and an access UL may be TDM-multiplexed in
one carrier frequency (that is, only one of the backhaul UL and the
access UL is active at a specific time).
[0120] Multiplexing of backhaul links in FDD is performed such that
backhaul DL transmission and backhaul UL transmission take place in
a DL frequency band and a UL frequency band, respectively. In
comparison, multiplexing of backhaul links in TDD is performed such
that backhaul DL transmission and backhaul UL transmission take
place in a DL subframe band between an eNB and an RN and a UL
subframe between the eNB and the RN, respectively.
[0121] In the case of an in-band RN, for example, if backhaul DL
reception from an eNB and access DL transmission to a UE are
performed simultaneously in the same frequency band, a signal
transmitted from the transmitter of the RN may be received at the
receiver of the RN. As a result, signal interference or Radio
Frequency (RF) jamming may occur at the RF front-end of the RN.
Likewise, if access UL reception from a UE and backhaul UL
transmission to an eNB take place simultaneously in the same
frequency band, the RF front-end of the RN may experience signal
interference. Therefore, simultaneous transmission and reception in
the same frequency band may not be feasible unless a reception
signal and a transmission signal are sufficiently isolated from
each other, for example, a Tx antenna is geographically apart
enough from an Rx antenna (e.g. on the ground/underground).
[0122] One way to handle the signal interference is to operate the
RN such that while the RN is receiving a signal from a donor cell,
it is not transmitting signals to UEs. That is, a gap is created in
RN-to-UE transmission and UEs (including legacy UEs) are not
supposed to expect any RN transmission during the gap. In FIG. 6, a
first subframe 1010 is a general subframe carrying a DL (i.e. an
access DL) control signal and data from an RN to a UE, and a second
subframe 1020 is a Multicast Broadcast Single Frequency Network
(MBSFN) subframe that carries a control signal from the RN to the
UE in a control region 1021 but does not carry a signal from the RN
to the UE in the remaining region 1022 of the MBSFN subframe. Since
a legacy UE expects reception of a PDCCH in every DL subframe (that
is, the RN needs to support legacy UEs' reception of a PDCCH and
measurement using the PDCCH within its coverage), a PDCCH needs to
be transmitted in every DL subframe, for reliable operation of the
legacy UEs. Accordingly, the RN needs to perform access DL
transmission, instead of backhaul DL reception, even in the first N
(N=1, 2 or 3) OFDM symbols of a subframe set for DL transmission
(i.e. backhaul DL transmission) from the eNB to the RN, that is, in
the second subframe 1020. In this context, a PDCCH is transmitted
from the RN to a UE in the control region 1021 of the second
subframe 1020, thereby providing backward compatibility to legacy
UEs served by the RN. While no RN-to-UE transmission takes place in
the remaining region 1022 of the second subframe 1020, the RN can
receive a signal from the eNB in the remaining region 1022. This
frequency partitioning prevents simultaneous access DL transmission
and backhaul DL reception at an in-band RN.
[0123] The second subframe 1020 being an MBSFN subframe will be
detailed below. The MBSFN subframe is basically a subframe for
MBMS. MBMS refers to a service of transmitting the same signal
simultaneously from a plurality of cells. The control region 1021
of the second subframe 1020 may be referred to as a relay
non-hearing period. During the relay non-hearing period, the RN
transmits an access DL signal without receiving a backhaul DL
signal. As stated before, the relay non-hearing period may be set
to be 1, 2 or 3 OFDM symbols long. The RN may perform access DL
transmission to a UE during the relay non-hearing period 1021 and
perform backhaul DL reception from the eNB in the remaining region
1022. Because the RN is not allowed to perform simultaneous
transmission and reception in the same frequency band, the RN takes
a certain time to transition from a Tx mode to an Rx mode.
Therefore, it is necessary to set a Guard Time (GT) in which the RN
can switch from the Tx mode to the Rx mode in a starting period of
the backhaul DL reception region 1022. When the RN performs
backhaul DL reception from the eNB and access DL transmission to a
UE, a GT may also be set for switching from the Rx mode to the Tx
mode of the RN. The length of the GT may be given as a time-domain
value, for example, k (k.gtoreq.1) time samples (T.sub.s) or one or
more OFDM symbols. If successive backhaul DL subframes are
configured for the RN according to a specific subframe timing
alignment relationship, a GT may not be defined or set in the last
part of a subframe. To maintain backward compatibility, the GT may
be defined only in a frequency area set for backhaul DL subframe
transmission (if a GT is set in an access DL period, legacy UEs may
not be supported). The RN may receive a PDCCH and a PDSCH from the
eNB in the backhaul DL reception period 1022 except for the GT. The
PDCCH transmitted to the RN by the eNB in the data region (the
transmission gap in FIG. 6) of the backhaul DL subframe may be
referred to as a Relay-PDCCH (R-PDCCH), distinguishably from a
conventional PDCCH.
[0124] Handover
[0125] In a wireless communication system, handover is a function
of enabling a UE to automatically tune to a new communication
channel of a neighbor eNB, for seamless communication, when the UE
moves out of the service area of a serving eNB and enters the
service area of the neighbor eNB in a call-connected state.
[0126] FIG. 7 illustrates a handover procedure.
[0127] If a condition set by a serving eNB is satisfied or upon
generation of a predetermined event, a UE transmits a measurement
report message to the serving eNB (S110). The serving eNB is a
network node connected to the UE before handover. If the serving
eNB determines from the measurement report message received from
the UE that handover is needed, the serving eNB decides on handover
(S115).
[0128] The serving eNB transmits a handover prepare message
including UE context information to a target eNB (S120). The target
eNB is an eNB that manages a new cell into which the UE moves by
handover. The UE context information includes information about the
Quality of Service (QoS) of a service that the serving eNB provides
to the UE, a radio bearer type, etc.
[0129] The target eNB determines whether to accept the handover
request, taking into account its available wired/wireless resources
(S125). The target eNB transmits resource allocation information
along with a new temporary ID (C-RNTI) for the UE to the serving
eNB (S130).
[0130] The serving eNB transmits a handover command to the UE
(S140) and starts to transmit user data to the target eNB. The UE
performs L1 signaling and L2 signaling in order to reconfigure a
radio environment including timing synchronization with the target
eNB (S150). The UE receives timing information from the target eNB
and then transmits a handover confirm message to the target eNB
(S160).
[0131] The target eNB transmits a handover complete message
indicating successful handover to the serving eNB (S170). Then the
serving eNB releases all resources from the UE. The target eNB
requests location update for the UE to a Core Network (CN) (S180).
The CN transmits user data previously directed to the serving eNB
to the target eNB by switching a path configuration for the UE
(S190). Upon completion of the handover procedure, the target eNB
becomes a new serving eNB for the UE.
[0132] Mobile Relay
[0133] A mobile relay is an RN that relays signal transmission and
reception between a macro eNB and a UE, like a general RN, but is
not fixed in position.
[0134] For example, an RN installed in a transportation means (a
car, a bus, a train, etc.) may be a mobile relay. A cell (i.e. a
mobile cell) covered by the RN installed in the transportation
means may cover the inside and vicinity of the transportation
means. Preferably, the mobile relay may serve mainly UEs inside the
transportation means.
[0135] Problems encountered with a service provided by a macro eNB
(or a fixed eNB) can be solved for a UE inside a transportation
means by deploying a mobile relay in the transportation means. For
example, the attenuation of a signal strength caused by the
transportation means, its windows, etc. may be overcome. In
addition, if a plurality of UEs move together, they may
simultaneously perform handover from a serving eNB to a target eNB.
With the use of a mobile relay, the multi-handover situation may be
readily handled based on group mobility.
[0136] Because the position of a mobile relay changes over time,
problems that a legacy system does not face may be produced. For
example, if a conventional handover procedure with no regard to a
mobile relay is still used, this may be unnecessary to both a UE
and a network. Accordingly, a method for solving this problem
should be provided, when a mobile relay is introduced.
[0137] FIGS. 8 and 9 illustrate exemplary handover situations that
may result from introduction of a mobile relay. For the convenience
of description, it is assumed in FIGS. 8 and 9 that the mobile
relay is installed in a bus and a macro eNB covers a bus stop.
[0138] FIG. 8 illustrates an exemplary handover situation in the
case where UE1 and UE2 are waiting for a bus at a bus stop.
[0139] In the example of FIG. 8(a), UE1 and UE2 are served by a
macro eNB and a mobile relay is moving toward UE1 and UE2.
[0140] FIG. 8(b) illustrates a situation in which the mobile relay
has arrived at the location of UE1 and UE2. In this case, each of
UE1 and UE2 may sense a strong signal from the mobile relay and
thus may report the reception of the strong signal to the serving
eNB (i.e. the macro eNB). If the serving eNB follows a conventional
handover procedure that is based on received signal strength, the
serving eNB may perform handover of UE1 and UE2 to the cell of the
mobile relay.
[0141] FIG. 8(c) illustrates a situation in which UE1 gets on the
bus but UE2 stays where it is. In this case, since UE1 gets on the
bus and moves along with the mobile relay, it is appropriate that
UE1 performs handover from the macro eNB to the mobile relay.
[0142] However, a signal received from the macro eNB gets stronger
than a signal received from the mobile relay, for UE2 that is not
aboard the bus in the example of FIG. 8(c). Therefore, UE2 will
perform handover from the mobile relay to the macro eNB. In this
case, handover of UE2 to the mobile relay that stays just a moment
and then leaves may be unnecessary and increase network load.
[0143] FIG. 9 illustrates an exemplary handover situation, in the
case where a bus carrying UE1 and UE2 arrives at a bust stop.
[0144] FIG. 9(a) illustrates a situation in which UE1 and UE2 are
served by the mobile relay and the mobile relay, UE1, and UE2 are
moving toward a bus stop.
[0145] FIG. 9(b) illustrates a situation in which the mobile relay,
UE1, and UE2 have arrived at the bus stop. In this case, both UE1
and UE2 may sense a strong signal from the macro eNB and may report
the reception of the strong signal to the serving eNB (i.e. the
mobile relay). If the serving eNB follows the conventional handover
procedure that is based on received signal strength, the serving
eNB may perform handover of UE1 and UE2 to the cell of the macro
eNB.
[0146] FIG. 9(c) illustrates a situation in which UE1 gets off the
bus but UE2 leaves on the bus. In this case, since the mobile relay
gets far from UE1 and UE1 is located within the coverage of the
macro eNB, it is appropriate that UE1 performs handover from the
mobile relay to the macro eNB.
[0147] However, as the transportation means carrying the mobile
relay gets farther from the macro eNB, a signal received from the
mobile relay gets stronger than a signal received from the macro
eNB, for UE2 that stays on the bus in the example of FIG. 9(c).
Therefore, UE2 will perform handover from the macro eNB to the
mobile relay. In this case, handover of UE2 to the macro cell where
UE2 stays just for a short time may be unnecessary and increase
network load.
[0148] As noted from FIGS. 8 and 9, if a handover situation (e.g. a
signal from an eNB other than a serving eNB is stronger than a
signal from the serving eNB) is related to a mobile relay (i.e. the
mobile relay is a serving eNB or a target eNB in the handover
situation) in the conventional handover procedure, a predicted
location of a UE needs to be considered additionally. In the
disclosure, handover from a mobile relay to an eNB or handover from
an eNB to a mobile relay will be referred to as `mobile relay
handover`.
[0149] For this purpose, a UE may determine whether to perform
mobile relay handover by determining whether to move along with the
mobile relay. Specifically, only when the UE determines whether to
perform handover, taking into additional account whether the UE
gets aboard a transportation means having the mobile relay, while
being served by an eNB or the UE gets off the transportation means,
while being served by the mobile relay, unnecessary handover
operations are reduced.
EMBODIMENT 1
[0150] In the case of mobile relay handover, a UE may notify a user
of the UE of availability of the mobile relay handover, receive an
input from the user (e.g. receive information indicating whether
the user has gotten on or off a vehicle having a mobile relay), and
transmit the user input to an eNB in an embodiment of the present
invention. The eNB may determine whether to perform handover for
the UE based on the received user input.
[0151] A mobile relay handover is possible, for example, when a
mobile relay approaches a UE and thus the UE measures a strong
signal from the mobile relay or when a UE moving along with a
mobile relay approaches an eNB (e.g. a macro eNB) and thus measures
a strong signal from the eNB.
[0152] Handover availability may be notified to a user in various
manners. For example, the user is prompted to answer a query of
whether handover to the mobile relay or handover to the eNB will be
performed, a query of whether the user will get on (or has gotten
on) the transportation means having the mobile relay, or a query of
whether the user will get off (or has gotten off) the
transportation means having the mobile relay.
[0153] If a user of a UE is aboard a transportation means having a
mobile relay, this implies that a predicted traveling route of the
UE is identical to a predicted traveling route of the mobile relay.
Likewise, if the user gets off the transportation means, this
implies that a predicted traveling route of the UE is different
from a predicted traveling route of the mobile relay. In this
context, the term `get-on` or `get-off`will be used from the
viewpoint of a UE in order to describe a state of the UE
briefly.
[0154] To minimize unnecessary notifications of availability of
mobile relay handover, when handover is not mobile relay handover
(i.e. either of a serving eNB and a target eNB is not a mobile
relay in handover), handover availability may not be notified to a
user. Only when a signal from an eNB other than a serving eNB is
kept at or above a predetermined strength for a predetermined time
or longer, the notification may be transmitted to the user.
[0155] The function of notifying the availability of mobile relay
handover may be activated or deactivated directly by the user or
transparently for the user according to a predetermined condition.
For example, if the user stays at a stop for a transportation means
for a predetermined time or longer, the function of notifying
handover availability may be activated. At the moment the user is
away from the stop for a predetermined time or longer, the function
of notifying handover availability may be deactivated.
EMBODIMENT 2
[0156] In another embodiment of the present invention, a user may
preliminarily register identification information about mobile
relays (or transportation vehicles having the mobile relays) in a
UE. In the event of handover to or from a mobile relay having
identification information registered to the UE, the UE may perform
mobile relay handover without asking the user whether to perform
handover (or asking the user whether the user has gotten
on/off).
[0157] For example, identification information about a mobile relay
(or identification information about a transportation means having
the mobile relay) may include information about a bus line number
or a subway line number (or a predicted route of a bus line or a
subway line), a vehicle identification number, a mobile relay
identification number (e.g. a cell ID), a traveling direction, a
time, a place, etc. A cell ID may be allocated to a mobile relay
such that the mobile relay is distinguished from a general eNB
(e.g. a macro eNB). For example, a specific part of total IDs
available as cell IDs may be defined as cell IDs for mobile relays.
In this case, it may be determined whether a cell is a mobile relay
cell simply by the cell ID of the cell.
[0158] The identification information about the mobile relay may be
a combination of one or more pieces of identification information.
For example, identification information may be configured for every
vehicle of a specific line such that handover may be performed
irrespective of a traveling direction, time, and place. Or
identification information may be configured such that handover is
performed only when a vehicle corresponds to a specific traveling
direction, a specific time, and a specific place from among all
vehicles of a specific line. Handover from another eNB to a mobile
relay or handover from a mobile relay to another eNB may be always
performed according to identification information about the mobile
relay.
[0159] For example, a UE may always attempt handover to a mobile
relay having identification information registered to the UE, on
the assumption that the user of the UE gets on a transportation
means having the mobile relay. If information about a specific time
zone (e.g. a commute time zone to work) and/or information about a
specific stop (e.g. a stop in the neighborhood of a user's house)
is additionally set, when a mobile relay satisfying this condition
approaches, the UE may always perform handover to the mobile
relay.
[0160] In another example, a UE may always attempt handover from a
mobile relay having identification information registered to the
UE, on the assumption that the user of the UE gets off a
transportation means having the mobile relay. If information about
a specific time zone (e.g. a commute time zone to home) and/or
information about a specific stop (e.g. a subway station in the
neighborhood of a user's house) is additionally set, when a mobile
relay satisfying this condition approaches another eNB, the UE may
always perform handover to the eNB.
[0161] While it has been described that handover is allowed based
on identification information listed in a white list, by way of
example, identification information may be listed in a black list
so that handover to or from mobile relays having the identification
information may be prohibited. In general, handover is allowed for
a mobile relay installed in a public transportation means only in
some cases. Therefore, identification information may be configured
in a white list.
[0162] As described before, pre-registered identification
information may be changed dynamically by a user.
[0163] The identification information may be stored in the UE
and/or a network. In the former case, the UE may be configured to
report handover-related information (e.g. measurement information)
to an eNB, only when a mobile relay matches the identification
information. Therefore, unnecessary handover is not performed. In
the latter case, although the UE reports handover-related
information to the network (e.g. a serving eNB), the serving eNB
may determine not to perform handover, if the handover-related
information does not match the user-registered identification
information.
[0164] A macro eNB related to handover to or from a mobile relay
(e.g. a macro eNB covering a specific bus stop or a specific subway
station) may prepare for authentication of the UE, to thereby
shorten time taken for handover.
EMBODIMENT 3
[0165] In another embodiment of the present invention, a UE may
determine whether its user is approaching or receding from a mobile
relay by means of a sensor of the UE and may perform handover to or
from the mobile relay based on the determination.
[0166] For example, the UE may determine whether the user has
gotten on or off a transportation means having the mobile relay by
sensing a signal from a specific signal generator installed at an
entrance/exit door of the transportation means through the sensor
of the UE. For example, if a transportation means having a mobile
relay is a bus, a UE having a bus card may determine whether its
user is getting on/off the bus by near-field communication with a
card reader installed in the bus. For this operation, a signal
generated from the signal generator or the card reader may include
identification information about the bus (e.g. line information
about the bus).
[0167] If departure and arrival times are preset as is the case
with a train, an aircraft, a ship, etc., the UE may determine
departure and arrival times of such a transportation means by
reading ticket information or receiving a readable electronic
ticket. In this case, if the departure or arrival time of the
transportation means comes near and thus a signal from a specific
eNB gets stronger during measurement of signals from neighbor eNBs
(in the case of get-on or get-off), the UE may perform handover to
the eNB (i.e. mobile relay handover). Or the UE may acquire
information about a departure location and a destination from the
ticket information and may perform mobile relay handover at a
departure or arrival time in the departure location or the
destination. For example, the UE may extract destination
information from the ticket information and may acquire information
about an eNB located in the destination directly or indirectly
through a query and response procedure with a server in a
network.
[0168] While it has been described that a UE senses a user's get-on
or get-off, reports the sensing to an eNB, and thus performs mobile
relay handover in the above example, it may be further contemplated
that a sensor installed along with a mobile relay (or a
transportation means having the mobile relay) senses the UE's
get-on or get-off and the network initiates a mobile relay handover
procedure based on the sensing. For example, if the UE gets on the
transportation means with the mobile relay, the mobile relay may
serve as a target eNB and may request handover of the UE to a
serving eNB. If the UE gets off the transportation means with the
mobile relay, the mobile relay may serve as a serving eNB and may
initiate a handover procedure to a target eNB (e.g. a macro eNB
covering a place where the UE gets off the transportation means).
In both cases, it is determined whether a user gets on/off without
intervention of the user and mobile relay handover is performed
based on the determination.
EMBODIMENT 4
[0169] The forgoing embodiments of mobile relay handover,
specifically an embodiment of receiving a user input indicating
whether a user gets on or gets off a transportation means having a
mobile relay (Embodiment 1), an embodiment of assuming that a user
gets on or gets off a transportation means having a mobile relay
whose identification information has been registered to a UE
(Embodiment 2), and/or an embodiment of sensing a user's get-on or
get-off (Embodiment 3) may be used as information that triggers an
operation other than handover.
[0170] For example, if it is determined that a user is aboard a
transportation means with a mobile relay, a UE may switch call
termination from a bell mode to a vibration mode or may execute an
application that provides line information about the transportation
means. In addition, the UE may acquire information about the
location of the transportation means and information about an
expected time to a destination in the transportation means by
exchanging signals with communication equipment such as the mobile
relay. The UE may further notify the user whether the destination
is near based on the acquired information.
[0171] If the UE determines that the user has gotten off the
transportation means with the mobile relay, the UE may switch from
an aboard operation mode to a normal operation mode set before
being aboard.
[0172] FIG. 10 illustrates a signal flow for a method for
performing mobile relay handover according to the present
invention.
[0173] In the illustrated case of FIG. 10, a serving eNB may be a
mobile relay and a target eNB may be a macro eNB, or a serving eNB
may be a macro eNB and a target eNB may be a mobile relay. Handover
related to a mobile relay is called mobile relay handover, as
stated before.
[0174] A UE may determine its state in relation to handover
(S1010). Briefly speaking, the state of the UE may be a state in
which mobile relay handover is allowed or not allowed.
Specifically, the UE may be placed in a first state where the
mobile relay and the UE are in the same predicted traveling route
(e.g. when the user of the UE will get on/has gotten on a
transportation means having the mobile relay) or in a second state
where the mobile relay and the UE are in different predicted
traveling routes (e.g. when the user of the UE will get off/has
gotten off the transportation means having the mobile relay).
[0175] The state of the UE may be determined according to the
foregoing various embodiments (e.g. a user input, preset
identification information, and UE's sensing) in step S1010.
[0176] The UE may transmit information indicating the determined
state in relation to mobile relay handover to the serving eNB
(S1020). The serving eNB may receive the information (S1030). The
UE may transmit the state information together with or separately
from a measurement of a neighbor eNB (e.g. in step S110 of FIG. 7)
in step S1020.
[0177] The serving eNB may determine whether to perform the UE's
handover based on the state information in relation to the mobile
relay handover, received from the UE (S1040). For example, in the
case where the serving eNB is a macro eNB and the target eNB is a
mobile relay, the serving eNB may determine to approve handover if
the UE and the mobile relay travel in the same predicted route and
may determine not to approve handover if the UE and the mobile
relay travel in different predicted routes. Or in the case where
the serving eNB is a mobile relay and the target eNB is a macro
eNB, the serving eNB may determine not to approve handover if the
UE and the mobile relay travel in the same predicted route and may
determine to approve handover if the UE and the mobile relay travel
in different predicted routes.
[0178] The serving eNB may transmit a handover command to the UE
based on the determination as to handover (S1050). If the serving
eNB determines to approve the handover, a procedure for securing
resources for the UE may be performed at the target eNB before step
S1050 (e.g. steps S120 and S130 in FIG. 7). If the serving eNB
determines not to approve the handover, step S1050 may not be
performed.
[0179] The UE that has received the handover command, the serving
eNB, and the target eNB may perform a subsequent operation of the
handover procedure (e.g. steps S150 to S190 in FIG. 7) (S1060).
[0180] To perform mobile relay handover according to the present
invention, the foregoing embodiments may be implemented
independently or two or more of them may be implemented in
combination. For clarity, a redundant description will be avoided
herein.
[0181] FIG. 11 is a block diagram of a UE and an eNB according to
the present invention.
[0182] Referring to FIG. 11, a UE 1110 may include an Rx module
1111, a Tx module 1112, a processor 1113, a memory 1114, and a
plurality of antennas 1115. The UE 1110 supports MIMO transmission
and reception through the plurality of antennas 1115. The Rx module
1111 may receive signals, data, and information from another device
(e.g. an eNB or an RN). The Tx module 1112 may transmit signals,
data, and information to another device. The processor 1113 may
provide overall control to the UE 1110.
[0183] The UE 1110 may be configured to perform mobile relay
handover. The processor 1113 of the UE 1110 may be configured to
report information about the state of the UE in relation to the
mobile relay handover to a serving eNB. The processor 1113 may also
be configured to perform the mobile relay handover based on a
handover command received from the serving eNB, as determined based
on the state of the UE by the serving eNB.
[0184] Besides, the processor 1113 of the UE 1110 may process
information received at the UE or information to be transmitted
from the UE. The memory 1114 may store processed information for a
predetermined time and may be replaced with a component such as a
buffer (not shown).
[0185] Referring to FIG. 11, an eNB 1120 may include an Rx module
1121, a Tx module 1122, a processor 1123, a memory 1124, and a
plurality of antennas 1125. The eNB 1120 supports MIMO transmission
and reception through the plurality of antennas 1125. The Rx module
1121 may receive signals, data, and information from another device
(e.g. a UE, another eNB, or an RN). The Tx module 1122 may transmit
signals, data, and information to another device. The processor
1123 may provide overall control to the eNB 1120.
[0186] The eNB 1120 may be configured to support mobile relay
handover. The processor 1123 of the eNB 1120 may be configured to
receive information about the state of a UE in relation to mobile
relay handover from the UE. The processor 1123 may also be
configured to determine the mobile relay handover based on the
state of the UE and transmit a handover command to the UE.
[0187] The eNB 1120 of FIG. 11 may be another eNB involved in the
mobile relay handover or may be a mobile relay.
[0188] Besides, the processor 1123 of the eNB 1120 may process
information received at the eNB 1120 or information to be
transmitted from the eNB 1120. The memory 1124 may store processed
information for a predetermined time and may be replaced with a
component such as a buffer (not shown).
[0189] The above UE and eNB may be configured to implement the
foregoing embodiments independently or two or more of them in
combination. For clarity, a redundant description will be avoided
herein.
[0190] The description of an eNB in FIG. 11 may apply to an RN as a
DL transmission entity or a UL reception entity, and the
description of a transmission and reception apparatus in FIG. 11
may apply to a UE or an RN as a DL reception entity or a UL
transmission entity.
[0191] The embodiments of the present invention may be achieved by
various means, for example, hardware, firmware, software, or a
combination thereof.
[0192] In a hardware configuration, the methods according to the
embodiments of the present invention may be achieved by one or more
Application Specific Integrated Circuits (ASICs), Digital Signal
Processors (DSP), Digital Signal Processing Devices (DSDPs),
Programmable Logic Devices (PLDs), Field Programmable Gate Arrays
(FPGAs), processors, controllers, microcontrollers,
microprocessors, etc.
[0193] In a firmware or software configuration, the methods
according to the embodiments of the present invention may be
implemented in the form of a module, a procedure, a function, etc.
Software code may be stored in a memory unit and executed by a
processor. The memory unit is located at the interior or exterior
of the processor and may transmit and receive data to and from the
processor via various known means.
[0194] The detailed description of the preferred embodiments of the
present invention is given to enable those skilled in the art to
realize and implement the present invention. While the present
invention has been described referring to the preferred embodiments
of the present invention, those skilled in the art will appreciate
that many modifications and changes can be made to the present
invention without departing from the spirit and essential
characteristics of the present invention. For example, the
structures of the above-described embodiments of the present
invention can be used in combination. The above embodiments are
therefore to be construed in all aspects as illustrative and not
restrictive. Therefore, the present invention intends not to limit
the embodiments disclosed herein but to give a broadest range
matching the principles and new features disclosed herein.
[0195] Those skilled in the art will appreciate that the present
invention may be carried out in other specific ways than those set
forth herein without departing from the spirit and essential
characteristics of the present invention. The above embodiments are
therefore to be construed in all aspects as illustrative and not
restrictive. The scope of the invention should be determined by the
appended claims and their legal equivalents, not by the above
description, and all changes coming within the meaning and
equivalency range of the appended claims are intended to be
embraced therein. Therefore, the present invention intends not to
limit the embodiments disclosed herein but to give a broadest range
matching the principles and new features disclosed herein. It is
obvious to those skilled in the art that claims that are not
explicitly cited in each other in the appended claims may be
presented in combination as an embodiment of the present invention
or included as a new claim by a subsequent amendment after the
application is filed.
INDUSTRIAL APPLICABILITY
[0196] The above-described embodiments of the present invention are
applicable to various mobile communication systems.
* * * * *